The present disclosure relates to an image forming apparatus including an electrifying member for electrifying an image carrier, and particularly to an image forming apparatus that can perform recovery process for reducing frictional resistance of the surface of the image carrier.
Conventionally, in an image forming apparatus using an electrophotographic process such as a laser printer or a digital multifunction peripheral, the surface of the photosensitive drum (image carrier) having photoconductivity is uniformly electrified by an electrifying device, an electrostatic latent image is formed by exposure with an exposing device, and the electrostatic latent image is developed into a toner image by a developing device. Next, the toner image is transferred onto the surface of the recording medium such as a paper sheet by a transfer portion, and the toner image is fixed to the surface of the recording medium by a fixing portion. Thus, the series of image forming process is finished. In addition, toner remaining on the surface of the photosensitive drum after the toner image transfer is removed by a cleaning portion, and further, remaining charge is eliminated using a charge elimination lamp, as necessary, as a preparation for a next image formation.
In recent years, an amorphous silicon (a-Si) photosensitive drum is widely used as the image carrier of the image forming apparatus. The a-Si photosensitive drum has a high degree of hardness and a superior durability, and characteristics as a photoreceptor is hardly deteriorated after using for a long period of time so that high image quality can be maintained. Therefore, the image carrier can be easily handled with low running cost, and it is superior with high safety to environment.
As to the image forming apparatus using such the a-Si photosensitive drum, it is known that an image deletion is apt to occur due to its characteristics. In other words, when electrification is performed using the electrifying device, discharge from the electrifying device generates ozone. The ozone decomposes components in the air, and hence ionic products such as NOx and SOx are generated. The ionic products are water soluble and stick to the photosensitive drum so as to enter in a coarse structure of approximately 0.1 μm on the surface of the photosensitive drum, and hence they cannot be removed by a cleaning system used in a general-purpose machine. Further, if they absorb moisture in the air, resistance of the surface of the photosensitive drum is decreased. Thus, potential lateral flow occurs at an edge part of the electrostatic latent image formed on the surface of the photosensitive drum, and as a result, an image deletion may occur.
Therefore, there is proposed a method of suppressing a decrease in the resistance of the surface of the photosensitive drum with a simple structure so as to reduce the image deletion, and there is known a method of performing a refresh mode at a predetermined timing, in which the photoreceptor is ground by interaction between developer containing abrasive (grinding toner) and a grinding member (a rubbing roller and a cleaning blade), so as to remove the products generated by ozone without using a heater or the like. In this method, developer is printed or developed when printing is not performed (in a start mode of the apparatus or in a standby mode after printing), and the developer is not transferred to the recording medium but is supplied to the grinding member in the photoreceptor unit so as to be used for grinding the surface of the photosensitive drum.
In addition, in recent years, instead of a corotron type or scorotron type electrifying device, a contact electrification type electrifying device with little generation of ozone is used, in which the electrifying member (an electrifying roller or the like) is disposed in contact with or close to the photosensitive drum so as to electrify the photosensitive drum. Among this type of electrifying members, there is one to which an oscillation voltage is applied, in which a DC voltage and an AC voltage are superimposed, so that the photosensitive drum is electrified, and there is known one that can set an appropriate peak-to-peak voltage value (Vpp) of a high accuracy AC voltage despite of environmental variation such as temperature and humidity or secular change of the photosensitive drum, the electrifying member, or the like.